A legal up to date Grand Theft Auto V copy is required to play Rage Multiplayer
If you pirated the game, there's no fix, buy the game as Rage Multiplayer does not support pirated versions of the game.
Try all of these following steps, not everything in this list will help, but 90% of the time one of these will resolve your issue
Verify your game files,
Reinstall RageMP
Make sure you have a clean game, no mods should be installed (To make troubleshooting easie